1. Field of the Invention
The present invention relates to a midsole of a shoe sole, particularly to a cushioning structure thereof.
2. Description of the Related Art
A shoe sole is required to have cushioning performance.
In a conventional shoe sole, in general, a landing shock at the time of walking is absorbed by dissipating energy through compression deformation of a midsole or the like. However, a sufficient cushioning property can not be obtained merely by the absorption (dissipation) of the energy through compression deformation, since the amount of the absorption is generally small.
On the other hand, if the midsole is made thick in order to make the dissipation of the energy large, the lightweight property of the shoe sole is lost.
FIG. 15 (a) is a perspective view of a cushioning part disclosed in Japanese Patent Laid-Open No. Hei8-38211.
This cushioning part 500 is made of gel, and is provided with notch portions 501 for allowing compression deformation at the time of compression deformation of the part 500. However, the notch portions 501 are not a significant factor in promoting shear deformation.
FIG. 15(b) is a cross-sectional vertical side view showing a cushioning structure disclosed in Japanese Patent Laid-Open No. Hei3-170102.
The cushioning structure shown in FIG. 15(b) is provided with a columnar part 510 made of gel, and a coil spring 511 fitted around the part 510 for storing repulsive xe2x80x9cspring-backxe2x80x9d energy at the time of kicking and going forward.
FIG. 15(c) is a perspective view showing a part of an orthopedic shoe sole disclosed in U.S. Pat. No. 4,217,907.
This part 520 is fixed to a heel of an outer sole. This part 520 includes a number of projecting ribs 521 arranged side by side in a circumferential direction. When receiving a repulsing force W from the ground, the projecting ribs 521 rotate part 520 in the direction of the arrow 522. The part 520 is for correcting and curing foot deformities by this rotation. Part 520 is made of a relatively hard material and is not designed to absorb shock.
FIG. 16(a) and FIG. 16(b) are a front view and a plan view respectively showing a projection 400 of a sole disclosed in Peterson (U.S. Pat. No. 5,782,014).
A midsole unit of Peterson is provided with the helical or screw-like projection 400. Groove 401 is provided around the projection 400 in a range xcex11 of rotation of 360 degrees or more, i.e., groove 401 completely circumscribes projection 400. Since projection 400 thus has a shape like a screw and if a compression load is applied vertically to projection 400, the projection 400 is vertically compression-deformed like a coil spring, i.e., there is only a minimal amount of shear deformation.
A cushioning structure disclosed in Japanese Patent Laid-Open No. 197503/2000 that includes a shearing transformation element at a rear foot portion of a midsole. The shearing transformation element is shear-deformed at the time of landing in such a manner that it falls forward. However, since the element is deformed in such a manner that it falls, it is difficult to apply this concept under the ball of the foot.
An object of the invention is to improve a cushioning property due to shear deformation by providing a new structure of a shoe sole.
In order to achieve the object, according to a first aspect of the invention, a midsole is provided between an outer sole and an upper that is suitable for absorbing a shock of landing that includes a thick plate-shaped or column-shaped cushioning portion. A plurality of grooves are formed on an outer peripheral surface of the cushioning portion. The respective grooves are helically formed around a substantially vertical axial line. The respective grooves are arranged substantially parallel with each other. A range xcex1 in which each of the grooves is formed is larger than about 15 degrees around the axial line and smaller than about 180 degrees around the axial line.
When compression load is applied to the cushioning portion in the vertical direction, a rotating force to twist the cushioning portion around the vertical axial line is applied to the cushioning portion. Thus, shear deformation along the horizontal plane perpendicular to the axial line is generated in the inside of the cushioning portion.
This shear deformation has a cushioning function (i.e. an absorption function of energy) much greater than normal compression deformation. In the case where the cushioning part is required to be thin, e.g., the ball of the foot, the cushioning function due to shear deformation is greater and more effective than the cushioning function created by compression thereon. Further, since this shear deformation is generated around the axial line, in the case where the cushioning part is provided at a thin place, it has the cushioning function greater than such shear deformation as causes deformation in a state of falling, and therefore, it is more effective.
In the invention, the xe2x80x9cmidsolexe2x80x9d is provided between an outer sole and an upper and has the cushioning function. The whole midsole may be integrally formed, or may be constructed by assembling a plurality of parts. Besides, the cushioning portion may be integrally formed with a midsole body, or may be constructed by a part different from the midsole body.
In the invention, the term xe2x80x9chelixxe2x80x9d denotes a line formed by simultaneously and continuously carrying out both rotation of a point around one axial line and translation thereof along the axial line. The term xe2x80x9chelicalxe2x80x9d means xe2x80x9chelix-likexe2x80x9d, that is, includes not only a case where the ratio of a rotation angle by the rotation to a movement amount by the translation is constant, but also a case where the ratio of the rotation angle to the movement amount is inconstant. Further, the xe2x80x9chelicalxe2x80x9d includes a locus formed by simultaneously carrying out the parallel movement of the translation, which accompanies the rotation, along the axial line, and the movement in a radial direction with respect to the axial line.
In the invention, since the plurality of helical grooves is provided in the cushioning portion or the cushioning part, a helical protrusion or convex portion (bank) is generally formed between the grooves.
In the case where the point is not moved in the radial direction, the groove and the convex portion become such groove and convex portion as those of a helical gear. In the case where the point is moved in the radial direction, in addition to the parallel movement along the axial line, the groove and the convex portion become such groove and convex portion as those of a helical bevel gear or a spiral bevel gear.
In the invention, it is preferable that a lead angle 0 between the groove and the horizontal plane is set within the range of 35 degrees to 60 degrees. In the case where the lead angle xcex8 is set within the range as stated above, since the projection between the grooves is deformed in such a manner that it largely falls, the cushioning performance becomes high.
According to a second aspect of the invention, a midsole provided between an outer sole and an upper and being suitable for absorbing a shock of landing includes a midsole body and a cushioning part (component).
The midsole body includes a cavity. The cushioning part is fitted in the cavity. The cushioning part is formed of an elastomer. Young modulus of a member constituting the cushioning part is set to be a value smaller than Young modulus of a member constituting the midsole body. The cushioning part includes a through hole passing through the cushioning part from its upper surface to its lower surface, so that it is formed into a ring shape having an outer peripheral surface and an inner peripheral surface. A plurality of grooves is helically provided on the outer peripheral surface of the cushioning part, the grooves being arranged substantially parallel with each other. A plurality of grooves is helically provided on the inner peripheral surface of the part, the grooves being arranged substantially parallel with each other.
In the second aspect, since the through hole is formed in the cushioning part, torsional rigidity around the axial line is small, and therefore, in the case where a rotating force is generated in the cushioning part, the amount of rotation of the cushioning part becomes large. Besides, the grooves are formed not only on the outer peripheral surface of the cushioning part, but also on the inner peripheral surface of the cushioning part. Accordingly, the rotating force generated in the cushioning part becomes high. As stated above, since the cushioning part is easily rotated, and the rotating force becomes high, the cushioning function of the cushioning part is remarkably improved.
In the invention, it is preferable that the xe2x80x9ccavityxe2x80x9d is generally made a closed space. As the structure of the xe2x80x9ccavityxe2x80x9d, in addition to a case where the closed space is formed in the midsole itself, there is also a case where a recess provided in the midsole is closed by an insole such as a cup insole to form the cavity. In the case where the cushioning part is housed in a sealed container made of soft resin, the cavity may be a space having an opening. Incidentally, the cushioning part may be constructed by sealing a liquid gel in the sealed container.
In the invention, as the material of the xe2x80x9ccushioning partxe2x80x9d, elastomer is used, and preferably a gel such as a silicone gel or a polyethylene gel is used. Besides, it is preferable that the hardness of the cushioning part is SRIS-C hardness (a value measured by a C-type hardness meter of Society of Rubber Industry, Japan Standard) of 35 degrees or less, and more preferably, it is set within the range of SRIS-C hardness of 10 degrees to 30 degrees.
The body portion of the midsole is formed of a foam of resin such as EVA (ethylene-vinyl acetate copolymer) or syndiotactic 1,2-polybutadiene, or a foam of rubber.
In general, it is preferable that the hardness of the cushioning part is set to be a value lower than the hardness of the midsole body by SRIS-C hardness of 2 degrees or larger.
Incidentally, although the hardness value is based on the SRIS-C hardness, a hardness value according to another measuring method can also be converted on the basis of a conversion reference value.
In the second aspect, in a case where the cushioning part is buried in the forefoot portion of the midsole or the rear foot portion, the shape of the cushioning part is set to be a thick plate shape having a thickness of 3 mm or more, a thick plate shape having a thickness of 5 mm or more, or a column shape having a low height as compared with a diameter. Incidentally, as long as a space is secured, the shape of the cushioning part may be a column shape having a high height as compared with a diameter, and may be, for example, a rectangular column shape in addition to a cylindrical shape or a taper cylindrical shape.
In the case where several (five or six) grooves and/or convex portions are provided substantially on the entire periphery of the outer peripheral surface of the cushioning part having the low height as compared with the diameter, the cushioning part becomes the shape like a helical gear.
Incidentally, in order to obtain large deformation by giving continuity to the shear deformation along the peripheral surface, it is preferable that the outer peripheral surface and the inner peripheral surface are made circumferential surfaces (cylindrical surfaces). Besides, it is preferable to form the grooves and the convex portions substantially on the entire periphery and continuously from the upper end of the part to the lower end.
In order to generate sufficiently large shear deformation in the cushioning part, in general, it is preferable to make the width of the convex portion wider than that of the groove, and in order that the cushioning part is deformed integrally with the convex portion, it is preferable that the convex portion is integral with the cushioning part.
According to a third aspect of the invention, a midsole provided between an outer sole and an upper and being suitable for absorbing a shock of landing includes a midsole body and a cushioning part.
The midsole body includes a cavity. The cushioning part is fitted in the cavity. The cushioning part is formed of elastomer. Young modulus of a member constituting the cushioning part is set to be a value smaller than Young modulus of a member constituting the midsole body. The cushioning part is formed to be a plate having an upper surface and a lower surface. A plurality of helical grooves and/or convex portions is formed on at least one of the upper surface and the lower surface of the cushioning part, and the thickness of the cushioning part at the groove and/or convex portion is gradually changed along the groove and/or convex portion.
In the third aspect, since the helical grooves and convex portions are provided on the upper surface or the lower surface of the cushioning part, the ratio of the movement of a helix point in the radial direction becomes remarkably larger than the ratio of the movement in the axial direction. Accordingly, the groove and the convex portion is turbinate.
According to a fourth aspect of the invention, a midsole provided between an outer sole and an upper and being suitable for absorbing a shock of landing includes a midsole body and a cushioning part.
The midsole body includes a cavity. The cushioning part is fitted in the cavity. The cushioning part is formed of elastomer. Young modulus of a member constituting the part is set to be a value smaller than Young modulus of a member constituting the midsole body. The cushioning part includes an upper surface and a lower surface. The midsole body includes a support surface for supporting the lower surface of the cushioning part in the cavity. A plurality of helical convex portions biting into the lower surface of the cushioning part, and/or a plurality of helical grooves into which part of the lower surface of the cushioning part is deformed to be embedded are/is formed on the support surface. When compression load is applied to the cushioning part in the vertical direction, the convex portions and/or grooves generate a rotating force to twist the cushioning part around an axial line substantially along a vertical line.
That is, in the fourth aspect, instead of forming the grooves and the convex portions in the cushioning part, they are formed on the surface of the cavity in the midsole body.
In the case where the cushioning part is molded from low hardness elastomer such as silicone gel, the molding becomes easier when the grooves and the convex portions are provided in the midsole body made of EVA or the like, rather than provided on the cushioning part.
Particularly, when the cushioning part is made flat plate-shaped, the cushioning part can be formed by merely punching a large flat plate by a cutting die such as a Thomson Diecut.
Incidentally, by combining the third and fourth aspects, the grooves and the convex portions may be provided on both the surface of the cavity in the midsole body and the cushioning part.
The invention would be more clearly understood from the following description of the preferred embodiments with reference to the accompanying drawings. However, the embodiments and the drawings are merely for illustration and description. The scope of the invention should be determined on the basis of claims. In the accompanying drawings, the same reference numerals in the plural drawings designate the same or like portions.